Process for making self improving aluminum alloys



Patented Feb. 23, 1932 UNITED STATES PATENT OFFICE PROCESS FOR MAKING SELF IMPROVING ALUMINUM ALLOYS 1T0 Drawing. Application filed January 25, 1930, Serial No. 428,550, and in Germany January 81,- 1928.-

The propert of a series of aluminum alloys to show se f improvement of their physical qualities by ageing, that is by simply being left at room temperature, in some cases after previous mechanical and thermal treatment or special heat treatment, has been re-. pea-tedly observed and has also been made use of in practice for a series of aluminum alloys, as for example in the sheet, drawn and other forms ofthe alloys duralumin, Aludur and so forth of German Patent 244,554 and in the cast all o s Alneon, Neonalium and so forth. According-to the statements in the Werkstoifhandbuch fiir Nichteisenmetalle,

Berlin 1927 J5, Alneon contains 75 to 90% aluminum, 2 to 3% copper, 22 to 7% zinc and 0.5 to 1% other alloy components, impurities and improving additions combined. Neonalium contains 86 to 94% aluminum, 14 to 6% copper and 0.4 to 1% otheralloy components,

' including the impurities and improving additions. -VVith all these alloys the view has been taken that what is to be aimed at is to obtain as far as possible mixed crystals which in close combination with the eutectic give a uniform' metallographic picture, since enclosure between the crystals of in edients not taken up must' have a harm ul effect on the intercrystalline coherence. Neverthe- 0 less it has not been possible to satisfy fully the needs of practice with any of these alloys and thus open up new uses for aluminum, in volving considerably hig stresses aid in particular high degree of kability as possessed for example by a good turning brass.

Since the workability is approximately proportional to the Brinell hardness, this makes it necessary to go above a Brinell number of about 120. It has become possible in alumi- 40 Iium foundries, especially in America, and particularly in the manufacture of pistons, to reach Brinell numbers up to 150 as a maximum, by heat treatment and quenching. This process is, however, expensive owin to the necessary furnaces and is not possible for large pieces, as for example the crank cases of acre-engines and the like, as the pieces warp and internal stresses are set up. Furthermore the new alloys Alneon and Neonalium, which do away with this heat treatment, accordin to published particulars only reach such va ues in part on the pointed parts. I

Extens'ive'investigation has made it possible to prepare alloys which without special treatment have a Brinell hardness of 170 and more immediately after casting, the hardness increasing u to 200 during self improvement (ageing It has, moreover, been found that enclosure of ingredients of the allo between the crystals does not act harmful y, at least as far as the Brinell hardness, the workability, resistance to abrasion, the bending strength, heat co-eflicient of expansion and hot hardness, are concerned. The hot hardness indeed approaches that of cast iron.

The average value of the heat co-eflicient of expansion between 20 and 300 C. is almost 19 to 20. This renders it possible to make parts of aluminum alloys for which hitherto only heavy metals could be used and thus to make valuable use of the low specific v gravity of aluminum.

The investigations have, moreover, shown a way of making the alloy independent of accidental conditions during its preparation, since the basis of the self improvement (age-' ing) hasbeen discovered. 'The view hitherto extensively held that the ageing can be attributed solely to the presence of magnesium silicide or calcium silicide or similar compounds has proved incorrect, since these compounds where present in certain alloys have been entirely without effect. Nevertheless it is not denied that their presence is an aid to the improvement in properties. The essential basis for self improvement resides, however, in the presence of intermetallic compounds of which one component must be an alkali oralkaline earth metal, while the other components must be metals most preferably of groups I and VI of the periodic' system or less preferably of groups VII and VIII. The prepared alloys show under the microscope an extremely fine structure even 5 with the highest magnification, and a stron interlocking of the individual components 9 the structure. The fundamental require ment for the desired purpose is, however, the formation of intermetallio compounds.

Components which do not satisfy this requirement are worthless and in some circumstances even harmful.

Metallographic investigation also shows that contrary to the View hitherto held, exactly those alloys in which the individual structural components occur not as mixed crystals or as eutectic alloys but freely in spherical or irregular form, for example tungsten, have a considerable influence on the desired properties and do not harm the cohesion as already pointed out. Any silicide present in any case acts as a strengthener as in the known alloys, but as pointed out above does not alone have the desired result.

Advantageously the preparation is carried out as follows. Heavy metals are added to molten commercial aluminum in the form of their commercially obtainable metal-aluminum alloys at temperatures which are so low that burning of the aluminum cannot take place. After complete solution of the added alloy, for example a magnesium alloy or metallic magnesium is added at a low temperature say 800 C. and immersed, preferably in such quantity that the content of magnesium calculated on the total quantity of metal is not more than 1.5%. The dross metal oxide) on the melt is not removed beore the addition ofthe magnesium but is only pushed aside and then Well mixed in. A part of the magnesium acts as a reducing agent while the remainder goes into solution as an ingredient of the alloy. In casting it has proved of advantage not to allow too slow cooling; nevertheless sudden quenching is generally not necessary. Only the usual care in normal melting is necessary therefore in preparing the alloy, which is an important advantage of the process.

According to the invention therefore the process consists in that, in order to produce intermetallic compounds of alkalies or alkaline earths with metals of groups I and VI to VIII of the periodic system, intermediate machines, shoe making machines and so forth.

Owing to the ease of manufacture and the possibility of accurate dispensing of the several ingredients it is possible to make any desired variations which can be suited in their properties to the particular use in view.

What I claim is 1. An aluminum alloy havin Brinell hardness of about 170 and a speci c gravity of about 3.15, consisting of the following ingredients in approximate weight proportions: chromium 2%, tungsten 1%, copper 15%, nickel 0.5%, magnesium 0.5%, manganese 2% and the remainder aluminum.

2. A process of making aluminum alloys, which consists in melting commercially obtainable metal-aluminum alloys at a sufliciently low temperature to prevent burning of the aluminum, then adding heavy metals to the melt, such metals being in approximate proportions 2% Cr, 1% W, 15% Cu, 0.5% Ni and 2% Mn, thereupon adding, after said heavy metals have been completely dissolved, 0.5% to 1.5% Mg at a temperature of about 800 C. A

In testimony whereof I afiix my si ature.

SIEGFRIED JUNG lANS.

alloys are added in the usual manner to the -balt are implied.

As an example, an alloy made as described above and containing in addition to aluminum 2% Cr. 1% W, 15% Cu, 0.5% Ni, 0.5% Mg and 2 Mn has a Brinell hardness of about 170 and a. specific gravity of about 

